High performance GeSi avalanche photodiode operating beyond Ge bandgap limits

Abstract

Avalanche photodiodes (APDs) having at least one top stressor layer disposed on a germanium (Ge) absorption layer are described herein. The top stressor layer can increase the tensile strain of the Ge absorption layer, thus extending the absorption of APDs to longer wavelengths beyond 1550 nm. In one embodiment, the top stressor layer has a four-layer structure, including an amorphous silicon (Si) layer disposed on the Ge absorption layer; a first silicon dioxide (SiO 2 ) layer disposed on the amorphous Si layer, a silicon nitride (SiN) layer disposed on the first SiO 2 layer, and a second SiO 2 layer disposed on the SiN layer. The Ge absorption layer can be further doped by p-type dopants. The doping concentration of p-type dopants is controlled such that a graded doping profile is formed within the Ge absorption layer to decrease the dark currents in APDs.

What is claimed is: 
     
       1. An avalanche photodiode, comprising:
 a silicon-based substrate with a buried oxide (BOX) layer, the substrate having a first side and a second side opposite the first side; 
 at least one bottom stressor layer disposed on the second side of the substrate and in contact with the BOX layer, with a cavity formed underneath the at least one bottom stressor layer; and 
 a multi-layer structure disposed on the first side of the substrate, comprising:
 at least one top stressor layer including an amorphous silicon (Si) layer, the at least one top stressor layer coupled to at least one metal contact of a first electrical polarity; and 
 a germanium (Ge) absorption layer on which the at least one top stressor layer is disposed such that the amorphous Si layer is in direct contact with the Ge absorption layer, 
 
 wherein the at least one top stressor layer is configured to increase a tensile strain in the Ge absorption layer such that absorption of the Ge absorption layer between 1550 nm and 1650 nm is increased. 
 
     
     
       2. The avalanche photodiode of  claim 1 , wherein the at least one top stressor layer further comprises:
 the amorphous silicon layer; 
 a first silicon dioxide (SiO 2 ) layer disposed on the amorphous Si layer; 
 a silicon nitride (SiN) layer disposed on the first SiO 2  layer; and 
 a second SiO 2  layer disposed on the SiN layer. 
 
     
     
       3. The avalanche photodiode of  claim 1 , wherein the Ge absorption layer comprises Ge, germanium-silicon (GeSi), or silicon-germanium-carbon (SiGeC). 
     
     
       4. The avalanche photodiode of  claim 1 , further comprising:
 a charge layer on which the Ge absorption layer is disposed, 
 wherein the charge layer comprises p-type Si, p-type GeSi, or p-type SiGeC. 
 
     
     
       5. The avalanche photodiode of  claim 4 , further comprising:
 a multiplication layer on which the charge layer is disposed, 
 wherein the multiplication layer comprises intrinsic Si or lightly doped n-type Si. 
 
     
     
       6. The avalanche photodiode of  claim 5 , further comprising:
 a contact layer on which the multiplication layer is disposed, 
 wherein the contact layer comprises n-type Si. 
 
     
     
       7. The avalanche photodiode of  claim 1 , wherein the at least one bottom stressor layer functions as a reflection layer and is configured to increase a tensile strain in the Ge absorption layer. 
     
     
       8. The avalanche photodiode of  claim 1 , wherein the multi-layer structure further comprises:
 a charge layer on which the Ge absorption layer is disposed; 
 a multiplication layer on which the charge layer is disposed; and 
 a contact layer on which the multiplication layer is disposed, the contact layer coupled to at least one metal contact of a second electrical polarity opposite to the first electrical polarity. 
 
     
     
       9. The avalanche photodiode of  claim 1 , wherein the Ge absorption layer further comprises p-type dopants, wherein a doping concentration of the p-type dopants is controlled such that a graded doping profile of the p-type dopants is formed within the Ge absorption layer, and wherein the p-type dopant comprises gallium (Ga) or boron (B). 
     
     
       10. The avalanche photodiode of  claim 1 , wherein the bottom stressor layer comprises a metal layer including aluminum, titanium, gold, silver, nickel, cobalt, platinum, or tungsten. 
     
     
       11. An avalanche photodiode, comprising:
 a silicon-based substrate with a buried oxide (BOX) layer, the substrate having a first side and a second side opposite the first side; 
 at least one bottom stressor layer disposed on the second side of the substrate and in contact with the BOX layer, with a cavity formed underneath the at least one bottom stressor layer; and 
 a multi-layer structure disposed on the first side of the substrate, comprising:
 at least one top stressor layer including an amorphous silicon (Si) layer, the at least one top stressor layer coupled to at least one metal contact of a first electrical polarity; 
 a germanium (Ge) absorption layer on which the at least one top stressor layer is disposed such that the amorphous Si layer is in direct contact with the Ge absorption layer; 
 a charge layer on which the Ge absorption layer is disposed; 
 a multiplication layer on which the charge layer is disposed; and 
 a contact layer on which the multiplication layer is disposed, the contact layer coupled to at least one metal contact of a second electrical polarity opposite to the first electrical polarity, 
 
 wherein the at least one top stressor layer is configured to increase a tensile strain in the Ge absorption layer such that absorption of the Ge absorption layer between 1550 nm and 1650 nm is increased. 
 
     
     
       12. The avalanche photodiode of  claim 11 , wherein the at least one top stressor layer further comprises:
 the amorphous silicon layer; 
 a first silicon dioxide (SiO 2 ) layer disposed on the amorphous Si layer; 
 a silicon nitride (SiN) layer disposed on the first SiO 2  layer; and 
 a second SiO 2  layer disposed on the SiN layer. 
 
     
     
       13. The avalanche photodiode of  claim 11 , wherein the charge layer comprises p-type Si, p-type GeSi, or p-type SiGeC, wherein the multiplication layer comprises intrinsic Si or lightly doped n-type Si, and wherein the contact layer comprises n-type Si. 
     
     
       14. The avalanche photodiode of  claim 11 , wherein the at least one bottom stressor layer functions as a reflection layer. 
     
     
       15. The avalanche photodiode of  claim 11 , wherein the at least one bottom stressor layer is configured to increase a tensile strain in the Ge absorption layer. 
     
     
       16. The avalanche photodiode of  claim 11 , wherein the Ge absorption layer further comprises p-type dopants, wherein a doping concentration of the p-type dopants is controlled such that a graded doping profile of the p-type dopants is formed within the Ge absorption layer, and wherein the p-type dopant comprises gallium (Ga) or boron (B). 
     
     
       17. The avalanche photodiode of  claim 11 , wherein the bottom stressor layer comprises a metal layer including aluminum, titanium, gold, silver, nickel, cobalt, platinum, or tungsten. 
     
     
       18. An avalanche photodiode, comprising:
 a silicon-based substrate with a buried oxide (BOX) layer, the substrate having a first side and a second side opposite the first side; 
 at least one bottom stressor layer disposed on the second side of the substrate and in contact with the BOX layer, with a cavity formed underneath the at least one bottom stressor layer; and 
 a multi-layer structure disposed on the first side of the substrate, comprising:
 at least one top stressor layer including an amorphous silicon (Si) layer, the at least one top stressor layer coupled to at least one metal contact of a first electrical polarity; 
 a germanium (Ge) absorption layer doped with p-type dopants on which the at least one top stressor layer is disposed, a doping concentration of the p-type dopants is controlled such that a graded doping profile of the p-type dopants is formed within the Ge absorption layer; 
 a charge layer on which the Ge absorption layer is disposed; 
 a multiplication layer on which the charge layer is disposed; and 
 a contact layer on which the multiplication layer is disposed, the contact layer coupled to at least one metal contact of a second electrical polarity opposite to the first electrical polarity, 
 
 wherein the at least one bottom stressor layer functions as a reflection layer and is configured to increase a tensile strain in the Ge absorption layer, and 
 wherein the amorphous Si layer is in direct contact with the Ge absorption layer. 
 
     
     
       19. The avalanche photodiode of  claim 18 , wherein the Ge absorption layer comprises Ge, germanium-silicon (GeSi), or silicon-germanium-carbon (SiGeC), and wherein the p-type dopant comprises gallium (Ga) or boron (B), and wherein the at least one top stressor layer further comprises:
 the amorphous silicon layer; 
 a first silicon dioxide (SiO 2 ) layer disposed on the amorphous Si layer; 
 a silicon nitride (SiN) layer disposed on the first SiO 2  layer; and 
 a second SiO 2  layer disposed on the SiN layer. 
 
     
     
       20. The avalanche photodiode of  claim 18 , wherein the bottom stressor layer comprises a metal layer including aluminum, titanium, gold, silver, nickel, cobalt, platinum, or tungsten.